Vibrational temperatures of CO 2 are studied in a pulsed glow discharge by means of time-resolved in situ Fourier transform infrared spectroscopy, with a 10 μs temporal resolution. A method to analyze the infrared transmittance through vibrationally excited CO 2 is presented and validated on a previously published CO 2 spectrum, showing good agreement between fit and data. The discharge under study is pulsed with a typical duty cycle of 5-10 ms on-off, at 50 mA and 6.7 mbar. A rapid increase of the temperature of the asymmetric stretch vibration (T 3 ) is observed at the start of the pulse, reaching 1050 K, which is an elevation of 550 K above the rotational temperature (T rot ) of 500 K. After the plasma pulse, the characteristic relaxation time of T 3 to T rot strongly depends on the rotational temperature. By adjusting the duty cycle, the rotational temperature directly after the discharge is varied from 530 to 860 K, resulting in relaxation times between 0.4 and 0.1 ms. Equivalently, as the gas heats up during the plasma pulse, the elevation of T 3 above T rot decreases strongly.

How dielectric, metallic and liquid targets influence the evolution of electron properties in a pulsed He jet measured by Thomson and Raman scattering.

A kinetic model describing the time evolution of ∼70 individual CO 2 (X 1 Σ + ) vibrational levels during the afterglow of a pulsed DC glow discharge is developed in order to contribute to the understanding of vibrational energy transfer in CO 2 plasmas. The results of the simulations are compared against in situ Fourier transform infrared spectroscopy data obtained in a pulsed DC glow discharge and its afterglow at pressures of a few Torr and discharge currents of around 50 mA. The very good agreement between the model predictions and the experimental results validates the kinetic scheme considered here and the corresponding vibration-vibration and vibration-translation rate coefficients. In this sense, it establishes a reaction mechanism for the vibrational kinetics of these CO 2 energy levels and offers a firm basis to understand the vibrational relaxation in CO 2 plasmas. It is shown that first-order perturbation theories, namely, the Schwartz-Slawsky-Herzfeld and Sharma-Brau methods, provide a good description of CO 2 vibrations under low excitation regimes.

This is the second of two papers presenting the study of vibrational energy exchanges in nonequilibrium CO 2 plasmas in low-excitation conditions. The companion paper addresses a theoretical and experimental investigation of the time relaxation of ∼70 individual vibrational levels of ground-state CO X 2 1 S + ( )molecules during the afterglow of a pulsed DC glow discharge, operating at pressures of a few Torr and discharge currents around 50mA, where the rate coefficients for vibration-translation (V-T) and vibration-vibration (V-V) energy transfers among these levels are validated (Silva et al 2018 Plasma Sources Sci. Technol. 27 015019). Herein, the investigation is focused on the active discharge, by extending the model with the inclusion of electron impact processes for vibrational excitation and de-excitation (e-V). The time-dependent calculated densities of the different vibrational levels are compared with experimental data obtained from time-resolved in situ Fourier transform infrared spectroscopy. It is shown that the vibrational temperature of the asymmetric stretching mode is always larger than the vibrational temperatures of the bending and symmetric stretching modes along the discharge pulse-the latter two remaining very nearly the same and close to the gas temperature. The general good agreement between the model predictions and the experimental results validates the e-V rate coefficients used and provides assurance that the proposed kinetic scheme provides a solid basis to understand the vibrational energy exchanges occurring in CO 2 plasmas.